1. Field of the Invention
The present invention relates to wafer metrology, and more particularly to optical metrology.
2. Related Art
Optical metrology involves directing an incident beam at a structure, measuring the resulting diffraction beam, and analyzing the diffraction beam to determine various characteristics, such as the profile of the structure. In semiconductor manufacturing, optical metrology is typically used for quality assurance. For example, after fabricating a periodic grating in proximity to a semiconductor chip on a semiconductor wafer, an optical metrology system is used to determine the profile of the periodic grating. By determining the profile of the periodic grating, the quality of the fabrication process utilized to form the periodic grating, and by extension the semiconductor chip proximate the periodic grating, can be evaluated.
Optical metrology systems can use various types of photometric devices, which include a light source and a detector capable of detecting the intensity of the diffracted light and converting the light into electrical signals. Conventional photometric devices used in optical metrology systems include reflectometers, which measures the change in the intensity of light, and ellipsometers, which measure the change in the intensity and polarization states of light. Additionally, various types of reflectometers (such as polarized reflectometers, unpolarized reflectometers, and the like) and ellipsometers (such as rotating polarizer ellipsometers (RPEs), rotating compensator ellipsometers (RCEs), phase modulated ellipsometers (PMEs), and the like) can be used.
While these various types of photometric devices convert light into electrical signals, each photometric device can provide the electrical signals as measured diffraction signals using various signal parameters. For example one type of reflectometer can provide measured diffraction signals using different signal parameters than another type of reflectometer. Additionally, two reflectometers that are the same type but made by different manufacturers can provide measured diffraction signals using different signal parameters. Thus, in conventional optical metrology systems, the hardware and software used to analyze the measured diffraction signals received from a photometric device are configured or calibrated to work with the particular photometric device being used, which can be time and cost prohibitive.